WEBVTT 00:00.000 --> 00:14.840 This is Hacker Public Radio episode 3,781 from Monday the 30th of January 2023. 00:14.840 --> 00:19.120 Today's show is entitled, The Jewel Thief. 00:19.120 --> 00:24.720 It is the 20th show of Andrew Conway and is about 13 minutes long. 00:24.720 --> 00:27.360 It carries a clean flag. 00:27.360 --> 00:40.720 The summary is, using the Joel Thief to suck energy out of flat batteries. 00:40.720 --> 00:45.280 Hello Hacker Public Radio people, this is McNallow also known as Andrew and today I'm 00:45.280 --> 00:49.760 going to tell you about a delightful little circuit called The Jewel Thief. 00:49.760 --> 00:58.320 The Joel Thief allows you to extract energy from an otherwise flat battery and more remarkably 00:58.320 --> 01:05.840 than that, using a flat battery, so I'll say I'm using a AA battery, it's was 1.5 volts 01:05.840 --> 01:12.640 when it started out its life, it's now down at around about 1 volt and even at 1 volt the 01:12.640 --> 01:19.920 Joel Thief's circuit is more than capable of allowing you to light up a two volt LED or need 01:19.920 --> 01:25.920 a string of LEDs of even higher voltage than that. 01:25.920 --> 01:35.280 So the magic of this circuit is that it's so simple as well as being able to use a flat battery 01:35.280 --> 01:46.080 to power an LED that requires a higher voltage and the secret of the circuit is very fast switching. 01:46.080 --> 01:50.880 So the LED isn't in fact on all the time, but it's on enough of the time that you can't really 01:50.880 --> 01:56.080 tell that it's flickering on and off. In fact, the circuit I've built as far as I can tell, 01:56.080 --> 02:02.400 it's flickering on and off 100 kHz, which is 100 000 times a second and I'm not going to pick 02:02.400 --> 02:14.400 that up with my eye certainly. So it only uses for components, the battery and for components, 02:14.400 --> 02:20.320 so I have a flat battery, and it's worth noting that when you I say a battery is flat, 02:20.720 --> 02:28.240 you will not be able to use it to power most things, but of course flat is relative. 02:28.240 --> 02:32.720 When a battery is exhausted, it's exhausted for the particular task that you put it to, for example, 02:32.720 --> 02:39.600 lighting up an LED torch, running a radio, running a Bluetooth mouth, Bluetooth mouse, 02:39.600 --> 02:46.080 I've got that right in the end. Once the voltage goes too low, without some degree pro-curry trickery, 02:46.080 --> 02:49.520 you can't use it anymore. But if what you really just want to do is light an LED, 02:50.080 --> 02:53.280 there is a way to coax remaining energy on the battery. Indeed, 02:53.280 --> 02:59.040 something like 50% of the energy in the battery is still there, it's just coming out to a low voltage, 02:59.040 --> 03:04.560 so if you can, put it to another use, that would be great. So let me just describe the circuit. 03:04.560 --> 03:09.600 So the four components are a resistor. The one I've got in front of me is a 10 kWh resistor, 03:09.600 --> 03:16.960 but I used a 1 kWh resistor to start with, and that would work too. I've got a transistor and 03:16.960 --> 03:24.160 NPN transistor, it's a BC-548, which is a totally bog-standard transistor, nothing fancy about 03:24.160 --> 03:31.840 that at all. A yellow LED, I guess, is a work with almost any color of LED, and the fourth, 03:31.840 --> 03:37.440 and most exciting component, is myself, one, and doctor. Now this is not an ordinary inductor. 03:37.440 --> 03:42.880 An ordinary inductor is a set, which is just a coil of wire around a ferromagnetic core, usually. 03:42.880 --> 03:48.000 This has a ferromagnetic core, it's in the shape of a torus, and most doctors will look like that. 03:48.000 --> 03:53.120 But the clever thing about this inductor is it's got two windings. One that goes one way around the 03:53.120 --> 03:58.080 torus, and another that goes the opposite way around the torus, and that's the key to how this 03:58.080 --> 04:04.800 thing works. It's actually quite easy, a little fiddly, to widen one of these yourself. So what I did, 04:04.800 --> 04:10.480 I had a dimmer switch for my kitchen light, it was a main voltage dimmer switch, 04:10.480 --> 04:18.320 that eventually looked up in through some LED driver circuits to all the lights in my kitchen. 04:19.280 --> 04:24.480 The switch on it became soft, so I had to replace it. But I don't like to throw things out, 04:24.480 --> 04:28.640 so I kept it thinking, let me keep him in handy one day, and indeed it did, because when I opened 04:28.640 --> 04:33.360 it up, I found it had an inductor. So I dismantled the inductor. Now a normal inductor just has, 04:33.360 --> 04:40.720 as I say, one winding of wire around the ferrite core. This is a ferrite bead, so it's a quite large 04:40.720 --> 04:46.720 actually, it's about centimeter across, and maybe a half a centimeter deep, and it's like a 04:46.720 --> 04:53.760 donut of some ferromagnetic material. So I removed just unwound by hand, so I'll start watching 04:53.760 --> 04:58.240 some television program, look to me a few minutes to unwind, about a meter worth of the wire 04:58.240 --> 05:05.440 that was well done to the inductor. Then I took this wire and folded it over, so I have two 05:06.400 --> 05:14.640 free ends, and the other end is now a fold, where the wire is folded in half. I anchored the two 05:14.640 --> 05:20.480 free ends by wrapping it around the ferrite bead once, and then proceeded to thread through 05:20.480 --> 05:30.960 the looped end, the folded end, repeatedly until I had windings that went all the way around 05:30.960 --> 05:36.640 the torus. Let's say, done that, I cut the wire at the fold, so I now have four 05:38.800 --> 05:45.680 ends, and using a multimeter, I actually, the next thing I did was I used a bit sandpaper 05:45.680 --> 05:50.080 to scrape off the enamel, because it's all, the wire is insulated, it would work as an inductor, 05:50.080 --> 05:56.720 if it was just bare copper wire, it's not, it's enameled wire. So at the ends, the four ends 05:56.720 --> 06:02.240 I had, I used sandpaper to scrape off that enamel, so I could make a electrical contact, and then 06:03.840 --> 06:13.680 what I did was I just joined two bits of wire that weren't connected to each other, and I used 06:13.680 --> 06:18.560 a multimeter to figure out which two ends didn't really matter, it doesn't matter which two ends, 06:18.560 --> 06:25.040 as long as they're not showing continuity in a multimeter, so I took those two ends and joined them 06:25.040 --> 06:33.200 together, and that will be the north north, the positive end of my, the inductor I'll use in the 06:33.200 --> 06:40.000 circuit. Now it's not an ordinary inductor, so it's got a common positive, and it's got two 06:40.000 --> 06:46.560 negative ends, if you like, and so what you do is you take the positive end and you connect that to 06:46.560 --> 06:56.480 your flat battery, so the positive terminal of your flat battery, one of the two negative ends, 06:56.480 --> 07:01.520 one of them gets connected to a resistor, and then that resistor gets connected to the base of the 07:01.520 --> 07:08.880 transistor, so the base of the transistor, if you imagine it, is like the tap that you can turn, 07:08.880 --> 07:13.360 so you can turn the transistor on and off, which will be crucial in a moment, so the base of the 07:13.360 --> 07:19.040 transistor controls where the current can flow through the rest of the transistor. The other 07:19.040 --> 07:28.240 negative wire that comes out in the inductor gets connected to the collector of the transistor, 07:29.200 --> 07:38.240 and the third and final leg of the transistor, the emitter gets connected to the negative terminal 07:38.240 --> 07:48.720 of the battery, and you also then take your LED and connect the positive leg of the LED to the 07:48.720 --> 07:54.400 collector, which is also connected to one of the ends of the negative end of the inductor, and 07:54.400 --> 08:00.000 that's the positive, so it's the positive end of the LED, negative leg of the LED gets connected 08:00.000 --> 08:09.760 to the emitter, and to zero volts, or the negative terminal of the battery. Look at the circuit diagram, 08:09.760 --> 08:14.160 it'll be easier than that, but this is the crucial bit, so what happens is when you connect all this 08:14.160 --> 08:20.800 up, current will flow from this flat battery, and it only needs a small amount, one volt is plenty, 08:21.520 --> 08:27.200 through a resistor, one kilotone tank alone doesn't matter, as tiny little current will flow 08:27.200 --> 08:34.880 into the base of the transistor, and then the transistor after a short delay will turn on. 08:35.840 --> 08:43.840 When the transistor turns on, it will allow current to flow through the other winding, so one winding 08:43.840 --> 08:48.720 of the inductor, remember, goes to the base of the transistor to open it up, the other winding 08:48.720 --> 08:56.160 comes down through the to the collector, and at first it can't the current can't flow that path, 08:56.160 --> 09:01.040 because the transistor is off, but once some current flows into the base through the other winding 09:01.040 --> 09:08.960 in the inductor, then the current can flow through the transistor, and it barely very low resistance, 09:08.960 --> 09:13.440 so very quickly, a much larger current will start to flow through the transistor, and a much larger 09:13.440 --> 09:19.120 current will start to flow through the other winding of the inductor, and because the two winding 09:19.120 --> 09:25.440 is the inductor, shear the same core, and they're winding opposite directions, what this does 09:26.800 --> 09:31.280 is it stops the current flowing into the base of the transistor, so what happens? Well, 09:31.280 --> 09:36.480 when that current stops, the transistor shuts off the tap, shuts, and then that main current 09:36.480 --> 09:43.200 path suddenly closes off, and this is the key property of an inductor, if you rapidly change 09:43.200 --> 09:48.880 the current flowing through an inductor, you get a spike in voltage, so the voltage, the 09:50.000 --> 09:56.560 inductor equation is voltage equals inductance times rate of change of current with time, so if you 09:56.560 --> 10:02.560 vary suddenly switch off the current, you'll get a spike in voltage, and so even when you're only 10:02.560 --> 10:08.400 got one say a one volt battery, you can easily produce two volts, three volts, four volts are 10:08.400 --> 10:14.960 potentially very large voltage is actually for a brief time, and that allows you to light 10:14.960 --> 10:19.120 the LED, which is connected across the collector no matter of the transistor. 10:20.880 --> 10:28.160 And as I said at the beginning, this happens extremely quickly. All of that takes place, 10:28.160 --> 10:34.080 say 100,000 times a second, depends on the value of the inductor, I've got quite a high value of 10:34.080 --> 10:41.840 inductor just because of what came out of the dimmer switch, and to a lesser extent it depends 10:41.840 --> 10:52.240 on the resistor, but really the switching as far as I understand it is mostly depend on the transistor, 10:52.240 --> 10:58.640 and the timings inside the transistor. Now the transistor that I'm using is not really designed 10:58.640 --> 11:02.480 for switching, and if you look at status sheet, it doesn't tell you anything about the timings, 11:02.480 --> 11:10.160 other transistors, MOSFETs, they do tell you stuff about timings, but this PC 548, no, 11:10.160 --> 11:13.520 you don't get any information, because it's not really intended for that, it doesn't matter, 11:13.520 --> 11:22.800 it just works. Now I have tried to understand the equations that governness and it's for such 11:22.800 --> 11:32.240 a simple circuit with four components, it's deceptively simple, because the equations are actually quite 11:32.240 --> 11:37.680 complex, so I actually went right back to Maxwell's equations, if you've done any physics you 11:37.680 --> 11:43.680 might have encountered Maxwell's equations, and I was able to derive the inductor equation in this case, 11:44.560 --> 11:51.120 and for those of you that are interested, it looks very much like the usual inductor equation, 11:51.120 --> 12:03.600 so the voltage drop across the inductor is equal to the inductor times the rate of change 12:03.600 --> 12:10.160 of the difference of the two currents that are flowing in the two's winding to the inductor. 12:11.760 --> 12:17.760 But actually to try and model what's going on in the circuit using that equation is difficult, 12:17.760 --> 12:23.440 because as I said earlier, it isn't the inductor in the resistor that is where the magic is 12:24.480 --> 12:29.120 happening, well some of the magic's happening in the inductor, a lot of the magic is happening in the 12:29.120 --> 12:34.720 transistor, and transistors are nonlinear devices, and if you don't have documentation and the 12:34.720 --> 12:41.200 time delays involved, I don't see really how you can model the joule thief in any simple way, 12:41.200 --> 12:47.120 you can certainly model it, but it's not simple, but it doesn't really matter, because if you want to 12:47.120 --> 12:55.040 just light up an LED with a flat battery, well a joule thief is certainly the way to go. 12:55.680 --> 13:01.680 Now if you would like to build your own, I highly recommend about half and half our video 13:01.680 --> 13:08.160 by Clive Mitchell or Big Clive, as he's known in YouTube, he is the person who coined the term 13:08.160 --> 13:13.840 joule thief, which is a lovely little pun, but the circuit itself is much older, it 13:13.840 --> 13:20.000 I think maybe the first patterns are almost 90 years ago, but those components are very different 13:20.000 --> 13:26.080 from the ones we would use today, and the ones I've got in front of me, and I think Clive references 13:26.080 --> 13:34.560 a letter in the magazine that was published in 1999, but anyway, for those details and for a lovely 13:34.560 --> 13:39.840 clear description and how to make it and how it works as well, do refer to Big Clive's video 13:39.840 --> 13:54.400 which is a link I'll put in the short notes. I hope you've found that, uh, interesting. Bye bye. 13:54.400 --> 13:59.280 You have been listening to Hecker Public Radio at Hecker Public Radio.org. 13:59.280 --> 14:05.280 Today's show was contributed by a HBO artist like yourself, if you ever thought of recording 14:05.280 --> 14:12.720 or cast, click on our contributing to find out how easy it means. Hosting Prage VR has been 14:12.720 --> 14:19.920 kindly provided by an onsthost.com, the Internet Archive, and our Sync.net. On this 14:19.920 --> 14:40.160 otherwise stages, today's show is released on our Creative Commons, Attribution, 4.0 International Bisones.